Mercaptan extraction



Patented Nov. 4, 1947 v I UNITED STATES PATENT OFFICE MERCAPTAN' EXTRACTION Richmond T. Bell, Highland Park, 111., assignor to The Pure Oil Company, Chicago, 111., a corporation of Ohio No Drawing. Application March 24, 1945, Serial No. 584,743

4 Claims. (Cl. 260-4509) 1 2 T is invention r at s to sepa at on of m pbons are extracted with caustic alkali-methanol ta from d res f mercaptans and hydrosolution containing approximately 5 to 30 per carbons. cent, and preferably to 30 per cent by weight In the p eparation of ercapt ns by re of water, mercaptans substantially free of hydroof olefinic hydrocarbons with hydrogen sulfide in 5 carbons can be separated from the mixture. In the presence of a catalyst, particularly a Frieclelthe absence of water, hydrocarbons dissolve in Crafts catalyst such as anhydrous aluminum the extract phase to alarge extent, greatly dechloride, fiuoboric acid, and mixtures of hydrogen creasing the degree of separation of mercaptans fluoride and boron trifluoride, there is formed a from th hydrocarbons. Although pure hydroreaetion pr t o p s d f ta s and 0 carbons are only slightly soluble in caustic alkaliunreacted olefins and other hydrocarbons which tha l l ti n, i th presence of large may have en present in the charging amounts of mercaptans a substantial proportion The mixture y contain from 10 p Cent of the hydrocarbons is dissolved in the extract or mo of r apt s. d p d on the Olefin hase. The difficulty in separating merca tans charging stock and the conditions under which from 1 11 1 even greater t t in separatthe reactlon is ed out. i ing parafrlns from mercaptans since the olefins W e e r p a a e synthesized from -in the presence of mercaptans are more soluble Olefimc Stock of lime boning range such as in caustic alkali-methanol solution than are polymer formed by solid phosphoric acid cataparamna However by adding Water to the lyzation of mixed butenes, separation of the resumng mercaptans from the hydrocarbons by caustic alkali-methanol solution the solubility of the hydrocarbons in the solution is decreased to fractional d1st11lat1on 1s difficult because of the a much greater extent than is the solubility of overlapping boiling points of the hydrocarbons and the mercaptans present in the mixture. Also, mercaptans W t result that mercaptans can Separation of mercaptans from hydrocarbons by be more efficiently separated from the hydrocarfractional distillation may be impractical where bonsthe mercaptan content of the mixture is low. In order demonstrate the invention hi invention is directed t process of ber of extractions wer made using caustic alkalirating mercaptans from admixtures with hydromethanol solutions containing different amounts carbonsby means of extraction. I have found 3 of water. The results of the extractions are set that if admixtures of mercaptans and hydrocarforth in the following table:

Table Per cent by Wt. of Hydro- Charging Stock Caustic Methanol Solution Extract Ralnnate carbons, based on charging stock, in-

ReLNo.

Per Per Quan- Per Per Pei Per Per Gm. Per cent Per cent cent Ex- Ratincent tity cent cent Gm. cent Gm. cent cent of Treated RS113 Used Hi0 CH5OH KOH IRSES ofCharge RSES Charge Rglcgvtract ate In the table the charging stock for run 1 was the reaction product prepared by reaction of copolymer produced by polymerization of C4 gases from an oil cracking operation in the presence of solid phosphoric acid catalyst at approximately 6001800 pounds per square inch and at temperatures of about 150-200" 0., and hydrogen sulfide at 25 C. and atmospheric pressure in the presence of anhydrous aluminum chloride.

Runs 2, 3 and 4 were made on the extract .iproduced in Run 1.

Runs 5, 6 and 7 were made on the reaction product prepared by reacting copolymers and hydrogen sulfide at 50 C. and atmospheric pressure in the presence of anhydrous aluminum chloride in mole ratio to unit charge of 1.0 to 7.76.

Runs 8, 9 and 10 were made on the reaction product prepared by reacting triisobutylene and hydrogen sulfide at 2458" C. and atmospheric pressure in the presence of anhydrous aluminum chloride.

Runs 11 to 15 were made on a blend of triisobutylene and l-dodecanethiol. The blend contained approximately 50% of each.

Runs 16 to 19 were made on triisobutylen'e used in producing the extraction charging stock for runs 8 to 10 and in the blends for runs 11 to 15.

By fractionation under vacuum it was determined that the mercaptans in the extraction charging stock for run 1 were principally dodecyl mercaptans with a lesser amount of octyl mercaptans. From a comparison of the sulfur contents of pure dodecyl mercaptans and pure octyl mercaptans, 15.84 and 21.96 per cent respectively, with the mercaptan-sulfur content of the charging stock for run '1, it is apparent that the charging stock contained a large proportion of unreacted hydrocarbons. Using a potassium Jhydroxide-methanol solution containing only 0.8 per cent by weight of water, 81 per cent by weight of the charge was dissolved in and subsequently recovered from the caustic alkalimethanol solution, whereas only 14.9 per cent remained undissolved. The balance of 4.2 per cent represents the loss incurred in the laboratory batch extraction procedure. The mercaptan-sulfur in the extract increased about 1.6

per cent over that in the charging stock.

Run 2 also demonstrates that a large portion of the hydrocarbons dissolved in the caustic alkali-methanol extract phase.

Run 3 made with a caustic potash-methanol solution containing 15.6 per cent by weight of water resulted in a much better separation between hydrocarbons and mercaptans, as shown bythe mercaptan sulfur content of the extract.

The separation between mercaptans and hydrocarbons was even more efiective in run 4, in

which an extract containing 15.73 per cent of mercaptan sulfur was obtained using an extract ing solution containing 29.5 per cent by weight of water. The mercaptan-sulfur content of this extract closely approached the theoretical value for dodecyl mercaptans. v

Runs 5, 6 and 7 were made on a charging stock containing a relatively low mercaptan content. As a result separation between hydrocarbons and mercaptans wasrgood with a caustic methanol solution containing as low as 6.4 per cent by weight of water. However, even in case of low mercaptan concentrations the separation improved by increasing the dilution with water as shown by comparison of runs 5, 6 and 7.

Runs 8, 9 and 10 show comparable results in i5 out extracting a mixture rich in mercaptans with a potassium hydroxide-methanol solution containing a fixed amount of potassium hydroxide and varying amounts of water. Here again a steady increase in mercaptan sulfur content of the extract appears with increase in the water content of the solvent.

Runs 11 to 15 are designed to show accurately the per cent of mercaptans actually extracted with different solutions, keeping in mind that l-dodecanethicl contains 15.8 per cent of sulfur. By comparing 'themercaptan-sulfur in the various materials with the theoretical amount present in pure l-dodecanethiol, the percentage of mercapitan in the particular product can be easily determined. In run 11 the extract contained about 46 per cent of hydrocarbons, whereas in run 15 the "extract contained about 27 per cent of hydrocarbons. I

Runs 16 to 19 are included to demonstrate the fact that in the absence of mercaptans, triisobutylene is only slightly soluble in caustic methanol solution regardless of the water content, although the same trend of decreasing solubility with increasing water content is apparent. In run 16 in which the caustic potash-methanol contained nowater, 'triisobutylene was only soluble to the extent of 4.1 per cent, whereas inrun 19 in which the caustic methanol contained 10 per cent of water, 'triisobutyl'ene was soluble to the extent of "0.7 per cent. Compare run 19 with run 14 in which 34.4 per cent of the extract was hydrocarbons although the extracting solvent contained 10 per cent of water.

Thus in order toobtain a merca'ptan .product containing a low hydrocarbon content it is necessary to use a caustic alkali-methanol solution containing in excess of 5 per cent and preferably in excess of 10per cent by weight of water, and not more than 30 per cent by weight of water. Water contents in excess of '30 per cent have very little more effect than solutions containing less than '30 per cent of water in concentrating the mercaptans in the extract, and give low yieldsbecause as the water content of the caustic a1- increases above this dissolve 'mercaptans -is kali-methanol solution amount the ability to greatly decreased.

causticalkali-me'thanol solutions which are satisfactory for the purpose of extracting mer- 'captans from admixtures with hydrocarbons are those containing approximately from 10 to 30 per cent by weight of caustic alkali. Solutions containing in excess of 30 per cent of caustic alkali are apt to cause emulsion difficultiea'ancl solutions containing less than 10 per cent of caustic alkali are not particularly efiective in extracting mercaptans. Although either sodium or potassium hydroxide-methanol solution may be used, I prefer to use potassium hydroxide solution since of the potassium hydroxide solution is greater than that of the caustic soda solution.

By subjecting a mixed hydrocarbon-'mercaptan product to a series of extraction steps with a series of caustic alkali-methanol solutions con v taining approximately 5 to 30 per cent of water with decreasing water content and increasing alkali content of the solutions as the 'merc'aptan content in the rafiinate becomes lower, substantially the entire mercapta-n content can be separated from the hydrocarbon content of the. product with very little contamination by hydro-'- carbons.

In carrying out the process I prefer to carry the extraction counter-currently in a suitable contact tower with a volume ratio of solvent to product to be extracted such that the amount of caustic alkali present in the caustic-methanol solution charged is at least per cent more than that equivalent to the mercaptan content of the product as charged. Where mercaptans are recovered from the spent caustic alkalimethanol solution by hydrolysis and distillation the quantity of excess alkali is of less importance than where mercaptans are recovered by neutralization of the spent caustic-methanol because the excess alkali is recovered unchanged in the former case whereas in the latter it is converted to a salt. The excess should preferably not exceed 100 per cent and generally need not be substantially more than about 10 per cent of the stoichiometric amount theoretically required for complete reaction with the entire mercaptan content of the product to be extracted. When neutralization is used to separate extract from solvent I prefer to use an acid, such as acetic or formic acid, as a neutralizing agent since less heat is evolved during neutralization and the alkali-metal salts are much more soluble in the resulting aqueous methanol phase than with a common mineral acid such as sulfuric acid.

The extracting process in accordance with my invention is generally carried out at normal room temperature, namely approximately 20 0., but as low temperatures as are consistent with satisfactory operation are preferred, depending principally upon the viscosities of fresh and spent solvent, and emulsion and separation difficulties. Higher temperatures such as 30 or 40 C., may be used, but extraction efficiencies generally are lower, other factors being equal, and losses may be higher.

My process is particularly useful in conjunction with vacuum fractionation in treating stocks in which the hydrocarbons present boil at temperatures close to the boiling point of the mercaptans present in the mixture, and in connection with separation of mercaptans from admixtures in which the mercaptans are present in low concentrations. In the latter case, an extract can be prepared having a high concentration of mercaptans, and this extract can be further concentrated by vacuum fractionation to obtain a mercaptan product meeting commercial requirements. By fractionating hydrocarbon-mercaptan mixtures under reduced pressure, mercaptans and hydrocarbons can be separated without decomposition of the mercaptans provided the mercaptans are not subjected to temperatures substantially greater than approximately 180 C,

Although my process is particularly useful in the separation of mercaptans of high molecular weight such as dodecyl and octyl mercaptans from hydrocarbons, it can be used for the separation of mercaptans of lower molecular weight such as butyl mercaptans, and admixtures of mercaptans, from hydrocarbons, both parailinic and olefinic.

It is claimed:

1. In a method of separating liquid mercaptans from mixtures with liquid hydrocarbons consisting chiefly of olefins containing twelve carbon atoms in the molecule in which mixture mercaptans are present in an amount of at least 25 per cent by weight, the step comprising contacting said mixture with a solution consisting of potassium hydroxide, methanol and water which solution contains approximately 10 to 30 per cent by weight of water and sufficient potassium hydroxide to react with all the mercaptans present but less than twice the stoichiometric equivalent of the mercaptans present in said mixture.

2. Method in accordance with claim 1 in which the mixture is extracted in a plurality of steps and the water content of the potassium hydroxide-methanol solution decreases in each successive step.

3. The method of preparing commercial grade mercaptans from a mixture composed chiefly of normally liquid olefins and mercaptans in which the latter are present in an amount of at least 25% by weight comprising extracting said mixture with a solution consisting of water, methyl alcohol and alkali metal hydroxide containing approximately 10 to 30 percent by weight of water and 10 to 30 percent by weight of alkali metal hydroxide, the quantity of solution being such that the amount of alkali metal hydroxide contained therein is up to per cent in excess of stoichiometric equivalent of the mercaptans in said mixture.

4. Method in accordance with claim 3 in which the mixture is extracted with successive batches of solution of decreasing water content.

RICHMOND T. BELL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,968,842 Malisofl Aug. '7, 1934 2,152,721 Yabroff Apr. 4, 1939 

